Illumination system particularly for microlithography

ABSTRACT

There is provided an illumination system for microlithography with wavelengths ≦193 nm. The illumination system includes a primary light source, a first optical component, a second optical component, an image plane, and an exit pupil. The first optical component transforms the primary light source into a plurality of secondary light sources that are imaged by the second optical component in the exit pupil. The first optical component includes a first optical element having a plurality of first raster elements that are imaged into the image plane, producing a plurality of images being superimposed at least partially on a field in the image plane. The second optical component comprises a first optical system that includes at least a third field mirror with positive optical power and a second optical system that includes at least a second field mirror with positive optical power. The first optical system images the plurality of secondary light sources in a plane between the first optical system and the second optical system, forming a plurality of tertiary light sources, and the second optical system images the plurality of tertiary light sources in the exit pupil.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is (a) a reissue of U.S. patent application Ser.No. 10/381,626, filed on Aug. 20, 2003, now U.S. Pat. No. 6,947,120,which is a U.S. national stage entry of International Application No.PCT/EP01/11233 , and (b) a continuation-in part of U.S. patentapplication Ser. No. 10/201,652. The PCT/EP01/11233 application wasfiled Sep. 28, 2001, and claims priority of U.S. patent application Ser.No. 09/679,718. The 10/201,652 application was filed Jul. 22, 2002, andis (a) a continuation-in part of U.S. patent application Ser. No.10/150,650, and (b) a continuation-in part of the 09/679,718application. The 10/150,650 application was filed May 17, 2002, and ,filed Sep. 28, 2001, which is a continuation-in-part of the U.S. patentapplication Ser. No. 09/679,718 application. The 09/679,718 applicationwas filed Sep. 29, 2000, issued as U.S. Pat. No. 6,438,199, and is acontinuation-in part of U.S. patent application Ser. No. 09/305,017. The09/305,017 application was filed May 4, 1999, and issued as U.S. Pat.No. 6,198,793. The present application is also claiming priority of (a)International Application No. PCT/EP00/07258, filed Jul. 28, 2000, (b)German Patent Application No. 299 02 108, filed Feb. 8, 1999, (c) GermanPatent Application No. 199 03 807, filed Feb. 2, 1999, and (d) GermanPatent Application No. 198 19 898, filed on May 5, 1998.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention concerns an illumination system for wavelengths ≦193 nm aswell as a projection exposure apparatus with such an illuminationsystem.

(2) Description of the Invention

In order to be able to further reduce the structural widths ofelectronic components, particularly in the submicron range, it isnecessary to reduce the wavelengths of the light utilized formicrolithography. Lithography with very deep UV radiation, so called VUV(Very deep UV) lithography or with soft x-ray radiation, so-called EUV(extreme UV) lithography, is conceivable at wavelengths smaller than 193nm, for example.

An illumination system for a lithographic device, which uses EUVradiation, has been made known from U.S. Pat. No. 5,339,346. For uniformillumination in the reticle plane and filling of the pupil, U.S. Pat.No. 5,339,346 proposes a condenser, which is constructed as a collectorlens and comprises at least 4 pairs of mirror facets, which are arrangedsymmetrically. A plasma light source is used as the light source.

In U.S. Pat. No. 5,737,137, an illumination system with a plasma lightsource comprising a condenser mirror is shown, in which an illuminationof a mask or a reticle to be illuminated is achieved by means ofspherical mirrors.

U.S. Pat. No. 5,361,292 shows an illumination system, in which a plasmalight source is provided, and the point plasma light source is imaged inan annular illuminated surface by means of a condenser, which has fiveaspherical mirrors arranged off-center.

From U.S. Pat. No. 5,581,605, an illumination system has been madeknown, in which a photon beam is split into a multiple number ofsecondary light sources by means of a plate with concave rasterelements. In this way, a homogeneous or uniform illumination is achievedin the reticle plane. The imaging of the reticle on the wafer to beexposed is produced by means of a conventional reduction optics.

EP-A-0 939 341 shows an illumination system and exposure apparatus forilluminating a surface over an illumination field having an arcuateshape with X-ray wavelength light. The illumination system comprisesfirst and second optical integrators each with a plurality of reflectingelements. The first and second optical integrators being opposinglyarranged such that a plurality of light source images are formed at theplurality of reflecting elements of the second optical integrator. Toform an arcuate shaped illumination field in the field plane accordingto EP 0 939 341 A2 the reflecting elements of the first opticalintegrator have an arcuate shape similar to the arcuate illuminationfield. Such reflecting elements are complicate to manufacture.

EP-A-1 026 547 also shows an illumination system with two opticalintegrators. Similar to the system of EP-A-0 939 341 the reflectingelements of the first optical integrator have an arcuate shape forforming an arcuate shaped illumination field in the field plane.

In EP-A-0 955 641 a system with two optical integrators is shown. Eachof said optical integrators comprises a plurality of raster elements.The raster elements of the first optical integrator are of rectangularshape. The arc shaped field in the field plane is formed by at least onegrazing incidence field mirror. The content of the above mentionedpatent-applications are incorporated by reference.

All systems of the state of the art, e.g. the systems according EP-A-0939 341 or EP-A-1 026 547 have the disadvantage that the track-length,of the illumination system is large.

It is therefore an object of the invention to overcome the disadvantagesof the illumination systems according to the state of the art and toprovide on illumination system for microlithography that fulfills therequirements for advanced lithography with wavelength less or equal to193 nm. The illumination system should be further compact in size andprovide a plane in which devices could be placed to change theillumination mode or to filter the radiation of the beams.

SUMMARY OF THE INVENTION

The system illuminates a structured reticle arranged in the image planeof the illumination system, which will be imaged by a projectionobjective onto a light sensitive substrate. In scanner-type lithographysystems the reticle is illuminated with a rectangular or arc-shapedfield, wherein a pregiven uniformity of the scanning energy distributioninside the field is required, for example better than ±5%. The scanningenergy is defined as the line integral over the light intensity in thescanning direction. The shape of the field is dependent on the type ofprojection objective. All reflective projection objectives typicallyhave an arc-shaped field, which is given by a segment of an annulus. Afurther requirement is the illumination of the exit pupil of theillumination system, which is located at the entrance pupil of theprojection objective. A nearly field-independent illumination of theexit pupil is required.

Typical light sources for wavelengths between 100 nm and 200 nm areexcimer lasers, for example an ArF-Laser for 193 nm, an F₂-Laser for 157nm, an Ar₂-Laser for 126 nm and an NeF-Laser for 109 nm. For systems inthis wavelength region refractive components of SiO₂, CaF₂, BaF₂ orother crystallites are used. Since the transmission of the opticalmaterials deteriorates with decreasing wavelength, the illuminationsystems are designed with a combination of refractive and reflectivecomponents. For wavelengths in the EUV wavelength region, between 10 nmand 20 nm, the projection exposure apparatus is designed asall-reflective. A typical EUV light source is aLaser-Produced-Plasma-source, a Pinch-Plasma-Source, a Wiggler-Source oran Undulator-Source.

The light of this primary light source is directed to a first opticalelement, wherein the first optical element is part of a first opticalcomponent. The first optical element is organized as a plurality offirst raster elements and transforms the primary light source into aplurality of secondary light sources. Each first raster elementcorresponds to one secondary light source and focuses an incoming raybundle, defined by all rays intersecting the first raster element, tothe corresponding secondary light source. The secondary light sourcesare arranged in a pupil plane of the illumination system or nearby thisplane. A second optical component is arranged between the pupil planeand the image plane of the illumination system to image the secondarylight sources into an exit pupil of the illumination system, whichcorresponds to the entrance pupil of a following projection objective

The first raster elements are imaged into the image plane, wherein theirimages are at least partially superimposed on a field that must beilluminated. Therefore, they are known as field raster elements or fieldhoneycombs.

All-reflective projection objectives used in the EUV wavelength regionhave typically an object field being a segment of an annulus. Thereforethe field in the image plane of the illumination system in which theimages of the field raster elements are at least partially superimposedhas preferably the same shape. The shape of the illuminated field can begenerated by the optical design of the components or by masking bladeswhich have to be added nearby the image plane or in a plane conjugatedto the image plane.

According to the invention the second optical component of theillumination system comprises a first optical system comprising at leasta third field mirror forming a plurality of the tertiary light sourcesin a plane conjugate to the exit pupil of the illumination system. Thetertiary light sources are imaged by a second optical system comprisingat least a second field mirror and a first field mirror into the exitpupil of the illumination system. The images of the tertiary lightsources in the exit pupil of the illumination system are calledquaternary light sources.

The field raster elements are preferably rectangular. Rectangular fieldraster elements have the advantage that they can be arranged in rowsbeing displaced against each other. Depending on the field to beilluminated they have a side aspect ratio in the range of 5:1 and 20:1.The length of the rectangular field raster elements is typically between15 mm and 50 mm, the width is between 1 mm and 4 mm.

To illuminate an arc-shaped field in the image plane with rectangularfield raster elements the first field mirror of the second opticalcomponent preferably transforms the rectangular images of therectangular field raster elements to arc-shaped images. The arc lengthis typically in the range of 80 mm to 105 mm, the radial width in therange of 5 mm to 9 mm. The transformation of the rectangular images ofthe rectangular field raster elements can be done by conical reflectionwith the first field mirror being a grazing incidence mirror withnegative optical power. In other words, the imaging of the field rasterelements is distorted to get the arc-shaped images, wherein the radiusof the arc is determined by the shape of the object field of theprojection objective. The first field mirror is preferably arranged infront of the image plane of the illumination system, wherein thereshould be a free working distance. For a configuration with a reflectivereticle the free working distance has to be adapted to the fact that therays traveling from the reticle to the projection objective are notvignetted by the first field mirror.

The surface of the first field mirror is preferably an off-axis segmentof a rotational symmetric reflective surface, which can be designedaspherical or spherical. The axis of symmetry of the supporting surfacegoes through the vertex of the surface. Therefore a segment around thevertex is called on-axis, wherein each segment of the surfaces whichdoes not include the vertex is called off-axis. The supporting surfacecan be manufactured more easily due to the rotational symmetry. Afterproducing the supporting surface the segment can be cut out withwell-known techniques.

The surface of the first field mirror can also be designed as an on-axissegment of a toroidal reflective surface. Therefore the surface has tobe processed locally, but has the advantage that the surrounding shapecan be produced before surface treatment.

The incidence angles of the incoming rays with respect to the surfacenormals at the points of incidence of the incoming rays on the firstfield mirror are preferably greater than 70°, which results in areflectivity of the first field mirror of more than 80%.

The second field mirror with positive optical power is preferably anoff-axis segment of a rotational symmetric reflective surface, which canhe designed aspherical or spherical, or an on-axis segment of a toroidalreflective surface.

The incidence angles of the incoming rays With respect to the surfacenormals at the points of incidence of the incoming rays on the secondfield mirror are preferably lower than 25°. Since the mirrors have to becoated with multilayers for the EUV wavelength region, the divergenceand the incidence angles of the incoming rays are preferably as low aspossible to increase the reflectivity, which should be better than 65%.With the second field mirror being arranged as a normal incidence mirrorthe beam path is folded and the illumination system can be made morecompact.

With the third field mirror of the second optical component the lengthof the illumination system can be reduced. The third field mirror isarranged between the plane with the secondary light sources and thesecond field mirror.

The third field mirror has positive optical power to generate images ofthe secondary light sources in a plane between the third and secondfield mirror, forming the tertiary light sources.

Since the plane with the tertiary light sources is arranged conjugatedto the exit pupil, this plane can be used to arrange masking blades tochange the illumination mode or to add transmission filters. Thisposition in the beam path has the advantage to be freely accessible.

To have not great distances between the second and third field mirrorand to reduce the refractive power at least of the second and thirdmirror the conjugated planes to the image plane in the second opticalcomponent are virtual conjugated planes. This means that there is noaccessible conjugated real image plane, in which the arc shaped field isformed in the second optical component.

This is advantageous for a compact design: Furthermore field mirrorswith low optical power are much easier to manufacture.

The third field mirror is similar to the second field mirror preferablyan off-axis segment of a relational symmetric reflective surface, whichcan be designed aspherical or spherical, or an on-axis segment of atoroidal reflective surface.

The incidence angles of the incoming rays with respect to the surfacenormals at the points of incidence of the incoming rays on the thirdfield mirror are preferably lower than 25°. With the third field mirrorbeing arranged as a normal incidence mirror the beam path can be foldedand therefore reduce the overall size of the illumination system.

To avoid vignetting of the beam path the first, second and third fieldmirrors are preferably arranged in a non-centered system. There is nocommon axis of symmetry for the mirrors. An optical axis can be definedas a connecting line between the centers of the used areas on the fieldmirrors, wherein the optical axis is bent at the field mirrors dependingon the tilt angles of the field mirrors.

With the tilt angles of the reflective components of the illuminationsystem the beam paths between the components can be bent. Therefore theorientation of the beam cone emitted by the source and the orientationof the image plane system can be arranged according to the requirementsof the overall system. A preferable configuration has a source emittinga beam cone in one direction and an image plane having a surface normalwhich is oriented almost perpendicular to this direction. In oneembodiment the source emits horizontally and the image plane has avertical surface normal. Some light sources like undulator or wigglersources emit only in the horizontal plane. On the other hand the reticleshould be arranged horizontally for gravity reasons. The beam paththerefore has to be bent between the light source and the image planeabout almost 90°. Since mirrors with incidence angles between 30° and60° lead to polarization effects and therefore to light losses, the beambending has to be done only with grazing incidence or normal incidencemirrors. For efficiency reasons the number of mirrors has to be as smallas possible.

The illumination system preferably comprises a second optical elementhaving a plurality of second raster elements. It is advantageous toinsert a second optical element with second raster elements in the lightpath after the first optical element with first raster elements, whereineach of the first raster elements corresponds to one of the secondraster elements. Therefore, the deflection angles of the first rasterelements are designed to deflect the ray bundles impinging on the firstraster elements to the corresponding second raster elements. The secondraster elements are preferably arranged at the secondary light sourcesand are designed to image together with the second optical component thefirst raster elements or field raster elements into the image plane ofthe illumination system, wherein the images of the field raster elementsare at least partially superimposed. The second raster elements arecalled pupil raster elements or pupil honeycombs. To avoid damaging thesecond raster elements due to the high intensity at the secondary lightsources, the second raster elements are preferably arranged defocused ofthe secondary light sources, but in a range from 0 mm to 10% of thedistance between the first and second raster elements.

By definition all rays intersecting the field in the image plane have togo through the exit pupil of the illumination system. The position ofthe field and the position of the exit pupil are defined by the objectfield and the entrance pupil of the projection objective. For someprojection objectives being centered systems the object field isarranged off-axis of an optical axis, wherein the entrance pupil isarranged on-axis in a finite distance to the object plane. For theseprojection objectives an angle between a straight line from the centerof the object field to the center of the entrance pupil and the surfacenormal of the object plane can be defined. This angle is in the range of3° to 10° for EUV projection objectives. Therefore the components of theillumination system have to be configured and arranged in such a waythat all rays intersecting the object field of the projection objectiveare going through the entrance pupil of the projection objective beingdecentered to the object field. For projection exposure apparatus with areflective reticle all rays intersecting the reticle needs to haveincidence angles greater than 0° to avoid vignetting of the reflectedrays at components of the illumination system.

In the EUV wavelength region all components are reflective components,which are arranged preferably in such a way, that all incidence angleson the components are lower than 25° or greater than 65°. Thereforepolarization effects arising for incidence angles around an angle of 45°are minimized. Since grazing incidence mirrors have a reflectivitygreater than 80%, they are preferable in the optical design incomparison to normal incidence mirrors with a reflectivity greater than65%.

The illumination system is typically arranged in a mechanical box. Byfolding the beam path with mirrors the overall size of the box can bereduced. This box preferably does not interfere with the image plane, inwhich the reticle and the reticle supporting system are arranged.Therefore it is advantageous to arrange and tilt the reflectivecomponents in such a way that all components are completely arranged onone side of the reticle. This can be achieved if the field lenscomprises only an even number of normal incidence mirrors.

The illumination system as described before can be used preferably in aprojection exposure apparatus comprising the illumination system, areticle arranged in the image plane of the illumination system and aprojection objective to image the reticle onto a wafer arranged in theimage plane of the projection objective. Both, reticle and wafer arearranged on a support unit, which allows the exchange or scan of thereticle or wafer.

The projection objective can be a catadioptric lens, as known from U.S.Pat. No. 5,402,267 for wavelengths in the range between 100 nm and 200nm. These systems have typically a transmission reticle.

For the EUV wavelength range the projection objectives are preferablyall-reflective systems with four to eight mirrors as known for examplefrom U.S. Ser. No. 09/503,640 showing a six mirror projection lens.These systems have typically a reflective reticle.

For systems with a reflective reticle the illumination beam path betweenthe light source and the reticle and the projection beam path betweenthe reticle and the wafer preferably interfere only nearby the reticle,where the incoming and reflected rays for adjacent object points aretraveling in the same region. If there are no further crossing of theillumination and projection beam path it is possible to separate theillumination system and the projection objective except for the reticleregion.

The projection objective has preferably a projection beam path betweensaid reticle and the first imaging element which is tilted toward theoptical axis of the projection objective. Especially for a projectionexposure apparatus with a reflective reticle the separation of theillumination system and the projection objective is easier to achieve.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below on the basis of drawings.

Here:

FIG. 1: A schematic view of an embodiment of an illumination systemaccording to the invention with two conjugated pupil planes.

FIG. 2: A detailed view of a projection exposure apparatus with aillumination system according to FIG. 1.

DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic view of a purely reflective embodiment of theinvention comprising a light source 8201, a collector mirror 8203, aplate with the field raster elements 8209, a plate with pupil rasterelements 8215, a second optical component 8221, a image plane 8229 and aexit pupil 8235. The second optical component comprises a first opticalsystem having a third field mirror 8225 and second optical system havinga second field mirror 8223. The third field mirror 8225 as well as thesecond field mirror 8223 have positive optical power. Furthermore thesecond optical component comprises a first field mirror 8227. The firstfield mirror 8227 is a grazing-incidence mirror with negative opticalpower for field shaping. In the purely reflective embodiment shown inFIG. 1 the field mirror 8225 and the field mirror 8223 are both concavemirrors forming an off-axis Gregorian telescope configuration. The fieldmirror 8225 images the secondary light sources 8207 in the planeconjugate to the exit pupil between the field mirror 8225 and the fieldmirror 8223 forming tertiary light sources 8259. In FIG. 1 only theimaging of the central secondary light source 8207 is shown. At theplane with the tertiary light sources 8259 conjugate to the exit pupil amasking unit 8261 is arranged to change the illumination mode of theexit pupil 8233. With stop blades it is possible to mask the tertiarylight sources 8259 and therefore to change the illumination of the exitpupil 8233 of the illumination system. Possible slop blades havecircular shapes or for example two or four circular openings, e.g. forquadropolar illumination. Alternatively or in addition to stop bladesalso transmission filters can be arranged in or near the plane withtertiary light sources. The field mirror 8223 and the field mirror 8227image the tertiary light sources 8259 into the exit pupil 8233 of theillumination system forming quaternary light sources 8235.

The optical axis 8245 of the illumination system is not a straight linebut is defined by the connection lines between the single componentsbeing intersected by the optical axis 8245 at the centers of thecomponents. Therefore, the illumination system is a non-centered systemhaving an optical axis 8245 being bent at each component to get a beampath free of vignetting. There is no common axis of symmetry for theoptical components. Projection objectives for EUV exposure apparatus aretypically centered systems with a straight optical axis and with anoff-axis object field. The optical axis 8247 of the projection objectiveis shown as a dashed line. The distance between the center of the field8231 and the optical axis 8247 of the projection objective is equal tothe field radius R_(field). The field mirrors 8223, 8225 are designed ason-axis toroidal mirrors, which means that the optical axis 8245 pathsthrough the vertices of the on-axis toroidal mirrors 8223, 8225 and8227. The second and the third field mirror 8223 and 8225 are normalincidence mirrors, which means that the incidence angles of the incomingrays with respect to the surface normals at the points of incidence ofthe incoming rays on the second and the third mirror are preferablylower than 25°.

The first field mirror 8227 is a grazing incidence mirror, which meansthat the incidence angles of the incoming rays with respect to thesurface normal at the points of incidence of the incoming rays on thefirst mirror are preferably greater than 70°.

In the embodiment depicted in FIG. 1 the second optical componentcomprising the first 8227, second 8223 and third field mirror 8225 hasonly virtual conjugate planes to the image plane 8229. This provides fora compact size of the second optical component with low refractive powerfor the field mirrors.

FIG. 2 shows an EUV projection exposure apparatus in a detailed view.Corresponding elements have the same reference numbers as those in FIG.1 increased by 200. Therefore, the description to these elements isfound in the description to FIG. 1. The illumination system according toFIG. 2 comprises instead of the normal incidence collector 8203 agrazing incidence collector 8403 with a plurality of reflectingsurfaces. Furthermore, for filtering the wavelength the illuminationsystem comprises a grating element 8404 and a diaphragm 8406. Anintermediate image 8408 of the primary light source 8401 lies at thediaphragm 8406. The system comprises as the system shown in FIG. 1 afirst optical element with first raster elements 8409 and a secondoptical element with second raster element 8415 and a second opticalcomponent with a first field mirror 8427, a second field mirror 8423 anda third field mirror 8425. The second field mirror 8423 and the thirdfield mirror 8425 are both concave mirrors. The field mirror 8425 imagesthe secondary light sources in the plane conjugate to the exit pupilbetween the field mirror 8425 and the field mirror 8423 forming tertiarylight sources. At the plane 8458 with the tertiary light sourcesconjugate to the exit pupil, a masking unit 8461 can be arranged tochange the illumination mode of the exit pupil. The field mirror 8423and the field mirror 8427 image the tertiary light sources into the exitpupil, not shown in FIG. 2, of the illumination system formingquaternary light sources.

The data for the optical components of the system according to FIG. 2are given in table 1. The components are shown in a y-z sectional view,wherein for each component the local co-ordinate system with the y- andz-axis is shown. For the field mirrors 8423, 8425 and 8427 the localco-ordinate systems are defined at the vertices of the mirrors. For thetwo plates with the raster elements the local co-ordinate systems aredefined at the centers of the plates. In table 1 the local co-ordinatesystems with respect to the local co-ordinate system of image plane isgiven. The tilt angle a about the x-axis of the local co-ordinate systemresults after the translation of the reference co-ordinate system in theimage plane into the local co-ordinate system. All co-ordinate systemsare right handed systems.

TABLE 1 Co-ordinate system of the optical components y z α R_(x) R_(y)K_(y) Intermediate image 8404 1031.11 −1064.50 38.9 Field rasterelements 8409 478.51 −379.65 32.75 −833.27 spherical Pupil rasterelements 8415 836.71 −1094.97 212.1 −972.9 spherical Third field mirror8425 104.54 −144.22 30.6 −264.68 −268.67 Conjugate plane to exit pupil164.59 −281.68 203.6 Second field mirror 8423 424.82 −877.31 208.9−831.34 spherical First field mirror 8427 −219.99 113.40 −5.05 −77.126hyperboloid −1.1479 Image plane 8429 0 0 0 Exit pupil −125 −1189.27 0

In the image plane 8429 of the illumination system the reticle 8467 isarranged. The reticle 8467 is positioned by a support system 8469. Theprojection objective 8471 having six mirrors images the reticle 8467onto the wafer 8473 which is also positioned by a support system 8475.The mirrors of the projection objective 8471 are centered on a commonstraight optical axis 8447. The arc-shaped object field is arrangedoff-axis. The direction of the beam path between the reticle 8467 andthe first mirror 8477 of the projection objective 8471 is tilted to theoptical axis 8447 of the projection objective 8471. The angles of thechief rays 8479 with respect to the normal of the reticle 8467 arebetween 3° and 10°, preferably 5° and 7°. As shown in FIG. 1 theillumination system 8479 is well separated from the projection objective8471. The illumination and the projection beam path interfere onlynearby the reticle 8467.

1. Illumination system, particularly for microlithography withwavelengths ≦ 193 nm, comprising: a primary light source; a firstoptical component; a second optical component; an image plane; and anexit pupil, wherein said first optical component transforms said primarylight source into a plurality of secondary light sources that are imagedby said second optical component in said exit pupil, wherein said firstoptical component includes a first optical element having a plurality offirst raster elements, that are imaged into said image plane producing aplurality of images being superimposed at least partially on a field insaid image plane, wherein said second optical component, comprises afirst optical system comprising at least a field mirror with positiveoptical power and a second optical system comprising at least a furtherfield mirror with positive optical power, wherein said first opticalsystem images said plurality of secondary light sources in a planebetween said first optical system and said second optical system forminga plurality of tertiary light sources, and wherein said second opticalsystem images said plurality of tertiary light sources in said exitpupil.
 2. The illumination system according to claim 1, whereinconjugated planes to the image plane in the second optical component arevirtual conjugated planes.
 3. The illumination system according to claim1, wherein the field mirror and the further field mirror form anoff-axis Gregorian telescope.
 4. The illumination system according toclaim 1, wherein said plane between said first optical system and saidsecond optical system is freely accessible.
 5. The illumination systemaccording to claim 1, further comprising a masking unit for changing anillumination mode, wherein said masking unit is arranged at or nearbysaid plurality of tertiary light sources.
 6. The illumination systemaccording to claim 1, wherein a transmission filter is arranged at ornearby said plurality of tertiary light sources.
 7. The illuminationsystem according to claim 1, wherein each of a plurality of raysintersects said further field mirror with an incidence angle lower than25° relative to surface normals.
 8. The illumination system according toclaim 1, wherein said further field mirror is an off-axis segment of arotational symmetric reflective surface.
 9. The illumination systemaccording to claim 1, wherein said further field mirror is an on-axissegment of a toroidal reflective surface.
 10. The illumination systemaccording to claim 1, wherein each of a plurality of rays intersectssaid field mirror with an incidence angle of less than 25° relative tosurface normals.
 11. The illumination system according to claim 1,wherein said field mirror is an off-axis segment of a rotationalsymmetric reflective surface.
 12. The illumination system according toclaim 1, wherein said field mirror is an on-axis segment of a toroidalreflective surface.
 13. The illumination system according to claim 1,wherein said plurality of first raster elements are rectangular, whereinsaid field is a segment of an annulus, and wherein said second opticalcomponent includes a field mirror for shaping said field to said segmentof said annulus.
 14. The illumination system according to claim 13,wherein said field mirror for shaping said field to said segment of saidannulus has negative optical power.
 15. The illumination systemaccording to claim 13, wherein each of a plurality of rays intersectssaid field mirror for shaping said field to said segment of said annuluswith an incidence angle greater than 70° relative to surface normals.16. The illumination system according to claim 13, wherein said fieldmirror for shaping said field to said segment of said annulus is anoff-axis segment of a rotational symmetric reflective surface.
 17. Theillumination system according to claim 13, wherein said field mirror forshaping said field to said segment of said annulus is an on-axis segmentof a toroidal reflective surface.
 18. The illumination system accordingto claim 13, wherein said first optical component further comprises asecond optical element having a plurality of second raster elements, andwherein each of said plurality of first raster elements corresponds toone of said plurality of second raster elements.
 19. The illuminationsystem according to the claim 18, wherein said plurality of secondraster elements and said second optical component image saidcorresponding plurality of first raster elements into said image plane.20. The illumination system according to claim 18, wherein saidplurality of second raster elements are concave mirrors.
 21. Aprojection exposure apparatus for microlithography comprising: theillumination system of claim 1; a reticle being located at said imageplane; a light-sensitive object on a support system; and a projectionobjective to image said reticle onto said light-sensitive object.